Modern circuit designs attempt to reduce power consumption. Power consumption is especially of concern in electronic devices that are intended for mobile use such as handheld devices such as video games, personal digital assistants, global positioning satellite receivers, as well as portable computers and wireless handsets. Since mobile devices typically operate using battery power, it is important to conserve power by limiting its dissipation whenever possible.
Examples of circuits in which power consumption considerations are important include graphics chips used in portable or laptop computers. Clearly, power consumption can be reduced by minimizing the number of components used in a given electronic device. Moreover, parts of a circuit may not be needed by an electronic device even when it is powered on. Therefore, power consumption can further be reduced by shutting down inactive parts, even while other parts are powered.
In graphics chips, for example, separate power supply pins may be available for the functional logic (referred to as core-logic) and the drivers for the input/output (I/O) pads. Therefore the core-logic may be shut down when not in use, while the I/O drivers continue to be powered.
Two types of power consumption called dynamic power consumption and static power consumption are typically considered. Dynamic power consumption results primarily from the switching of logic gates and the attendant charging and discharging of capacitors. In contrast, static power consumption is primarily caused by leakage current.
Although dynamic power consumption has been the focus of power reduction efforts for decades, shrinking die sizes and increasing number of transistors in newer manufacturing technologies, such as 0.1 micron and smaller technologies, have made static power dissipation equally important.
As static power dissipation is caused by leakage current, it cannot be materially reduced by reducing switching. However, shutting down inactive component helps in its reduction.
Unfortunately, shutting down parts of a circuit, and powering them back may cause spurious transient signals (called “glitches”) on electrical interconnections to internal circuit blocks, or interconnected external components.
For example, transient voltage signals may be observed on signal lines interconnected to the I/O pads of an integrated circuit when its core-logic is shut down first and then powered back up. This in turn may interfere with the operation of other interconnected integrated circuits.
Accordingly, there is a need for better circuit designs that reduce static power dissipation while reducing undesirable spurious signals which may affect the performance of interconnected components.